One can only guess where or if the Xantrex monitor was installed properly, or if the wind
gen was added in afterwards, etc.
Win generators need a "dump regulator" which is very different from the internal regulator
in a "car" alternator. If the wind
gen is running, and your engine alternator was correctly set up with a voltage sense lead, it will see the voltage from the wind gen and promptly turn itself off--making any use of the engine to charge a near total waste at that point.
So...you really need to trace it all out and see what accomodations were made to having all the bits play together nicely. Could be there's nothing wrong except the kids
aren't playing nicely in the sandbox.
Internal regulators in "car" alternators are oddly enough not designed to CHARGE your battery
, they are designed to NOT OVERCHARGE a battery during long runs. So they quickly drop back from full output (designed to replace what your starter pulled) to nearly idle output, unless there's something else sucking down voltage. A proper external regulator will outperform them--but you'd want one that also integrates or accomodates the wind generator
. Or, not use the wind gen and engine charging
at the same time.